Reply To: all my faces are 3d what happened?

Could it be that you weren’t in Wireframe Mode when you selected (maybe with Box Select), what looked like all the Faces:

but that way you only selected the ‘front’/visible Faces and whebn you then moved them, some were left behind:

I have done this sooo often and sometimes it still happens to me 😉 When I’m in luck I notice it immediately, but sometimes….

The opposite also happens: there is something (out of view) still selected when you move some part of your mesh and that gets moved with it unintentionally.